1. Field of the Invention
This invention generally relates to a method for image processing, and more particularly improvement in the modulation transfer function of an image.
2. Description of the Prior Art
Recently, apparatuses for capturing an image are popular and quite a few exist, e.g. a scanner, a digital camera, etc. A light sensing device captures light through optical lenses, which an object radiates or reflects from another light source, and obtains a formation of image of the object. A CCD (charge-coupled device, CCD) device or a CMOS (complementary metal-oxide-semiconductor) device is a common light sensing device that can capture the light to transfer an image digital data.
The image data can not be completed equal to that which is seen with the human eye, due to physical limitations or defects of the apparatus. For example, the modulation transfer function of the captured image reduces the result from an insufficient contrast, a blurred formation of images and so forth. The limitations are diffraction, aberrations, chromatism, and the scattering from an external light source and so on. Some limitations can be solved by means of amending the design of the apparatus. For example: amending the curvature of the lenses or the optic axis to solve the aberration; changing the material or the combination of lenses to solve the chromatism; employing rough inner surfaces on the apparatus and spreading black material on the inner surfaces thereof to reduce the scattering of external light. Although, this handling improves the quality of the captured image, but it can not totally overcome the effects and limitations thereof. The captured image still debases a definition and a contrast with the effects.
The original data (equal to that which is seen with the human eye) of the image is not destroyed but hidden by the effects, e.g. a difference in the brightness between pixels in a border between an object and the background of the image. The ratio in brightness relatively becomes smaller and not so obvious, due to joining the effect into the original data. Hence, the captured image is blurred. The image data comprises the original data and the unneeded external data.
The advantage of the digital image is that the digital image can function with a logical operation and a logical analysis. Hence, the digital image can be processed with software for enhancing the contrast or increasing the brightness thereof. Nevertheless, the image with enhanced contrast increases the difference in brightness and aliasing, which then becomes non-distinct due to processing the contrast thereof.
To eliminate external data is hard. The characteristics of external data do not affect the difference between pixels in the original data of the image. Furthermore, the digital image can function with a logical operation to amend the image data. Therefore, the border between an object and the background of the image can be determined with the characteristic and then the border therebetween is processed for amending the border. Moreover, the amending process is only processed with the border therebetween and not with the object and the background in the image. Hence, the amending process does not change the data of the image expect the border and does not cause a problem with aliasing. In the conventional art, the border is determined with 9 pixels, but in the present invention, the border can be determined with less pixels and the efficiency of the operation is improved.